1. Field of the Invention
The present invention relates generally to communication systems. More particularly, the present invention relates to Digital Subscriber Line (xe2x80x9cDSLxe2x80x9d).
2. Background
With the tremendous and emerging growth in various areas depending on data communications, such as Internet access, LAN access, broadcast TV, home shopping and video on demand, the need to provide faster data communication speeds has become crucial. However, traditional technologies such as analog modems have failed to provide the desired increase in speed and as a result more and more users are moving towards new technologies, such as DSL, which provides fast connection speeds. DSL refers to a class of technology used to obtain more bandwidth over existing telephone lines. Some DSL implementations also allow simultaneous voice and high-speed data.
FIG. 1 illustrates an example block diagram of a DSL communication system 100. The communication system 100 provides a communication link between a CPE (xe2x80x9cCustomer Premises Equipmentxe2x80x9d) 110, such as a personal computer, at one end and a computer network, such as an ISP (xe2x80x9cInternet Service Providexe2x80x9d) 145, at the other end. As shown, the communication between the CPE 110 and the ISP 145 occurs via copper wires or local loops 125 that terminate at the central office (xe2x80x9cCOxe2x80x9d) on the telephone company side and, at the other side, reach out to every home and business. The CO is the front line of the telecommunications network and may be described as a network node on the PSTN (xe2x80x9cPublic Switched Telephone Networkxe2x80x9d).
As further shown in FIG. 1, DSL technology is used in the communication system 100 to deliver communication services to the CPE 110 via the local loop 125. DSL can support a wide variety of high-bandwidth applications, such as high-speed Internet access, telecommuting, virtual private networking and streaming multi-media content. The end-to-end DSL-based communication system 100 includes the following sub-components: the CPE 100, the remote DSL Transmission Unit (xe2x80x9cDTU-Rxe2x80x9d) 120, the central DSL Transmission Unit (xe2x80x9cDTU-Cxe2x80x9d) 135 and the ISP 145.
DSL is a digital form of data communications that dramatically increases the digital capacity of ordinary telephone lines or the local loops into the homes or offices. Digital communication is the exchange of information in binary form. Unlike an analog signal, a digital signal does not use continuous waves to transmit information. Instead, DSL transmits data using discrete signals, for example, on and off states of electrical current. DSL provides an always-on operation in which digital data does not travel through the Public Switched Telephone Network (xe2x80x9cPSTNxe2x80x9d), but instead, at the CO, digital data is aggregated in a DSL Access Multiplexer (xe2x80x9cDSLAMxe2x80x9d) and forwarded to the appropriate ISP or data network. DSL has many flavors. High Bit Rate DSL (xe2x80x9cHDSLxe2x80x9d) is a symmetric technology, which provides the same transmission rate in both downstream and upstream directions. Symmetric DSL (xe2x80x9cSDSLxe2x80x9d) is an HDSL variation that uses only one cable pair and is offered in a wide range of speeds from 144 Kbps to 1.5 Mbps. SDSL is a rate adaptive technology. Asymmetric DSL (xe2x80x9cADSLxe2x80x9d) is a DSL flavor that shares the same line as the telephone, since it uses higher frequencies than the voice band. A version of ADSL is known as G.lite. Other flavors of DSL include Rate Adaptive DSL (xe2x80x9cRADSLxe2x80x9d) that adjusts speed based on line quality, Very High Bit Rate DSL (xe2x80x9cVDSLxe2x80x9d) that is an asymmetric version used as the final drop from a fiber optic junction, and ISDN DSL (xe2x80x9cIDSLxe2x80x9d). The specifications for these and other flavors of DSL are hereby incorporated by reference.
The CPE 110 may contain one or more PCs or workstations. Typically, multiple PCs reside on a LAN. The gateway to the external network can be a dedicated hardware, such as a router or a PC server acting as a router or proxy server. The DSL system at the CPE 110 side (or the DTU-R 120) and the DSL system at the central site (or DTU-C 135) form a DSL access network and are connected via the local loop 125. As shown, the access multiplexer system and the central site modems are usually combined into a single unit or DSLAM 130. As further shown, the communication system 100 may also use a Layer-2 protocol, such as Asynchronous Transfer Mode (xe2x80x9cATMxe2x80x9d) at the two ends of the DSL access network, namely modules 115 and 140. Like packet switching for data, ATM integrates the multiplexing and switching functions and allows communications between devices that operate at different speeds. The most basic service building block is the ATM virtual circuit, which is an end-to-end connection that has defined end points and routes but does not have bandwidth dedicated to it. Bandwidth is allocated on demand by the network as users have traffic to transmit. ATM is a set of international interface and signaling standards defined by the International Telecommunications Union (xe2x80x9cITUxe2x80x9d) that is hereby incorporated by reference.
One major drawback of the conventional DSL communication systems, such as the communication system 100, is that it takes a very long time to establish a connection between DTU-C 135 and DTU-R 120 at an optimal rate. Using DSL techniques, the training time is longer the slower the speed is. For example, with a line speed of 160 Kbps, the training may take about 60 seconds, whereas at a line speed of 1,552 Kbps, the training time may be reduced to about 11 seconds. Conventionally, in order to achieve an optimal data rate, DSL providers utilize a brute force technique, which requires training at a low rate and re-training at higher data rates, one by one, until the optimal rate is determined. However, such technique is extremely undesirable, as it is extremely time consuming and may take about 5 to 10 minutes before the optimal rate may be determined.
Another shortcoming of the conventional DSL communication systems is the pre-configuration of DTU-C 135 and DTU-R 120 at customer requested speeds, e.g., 160 Kbps, 192 Kbps and 384 Kbps. As a result, if the customer decides to change the requested speeds, the DSL provider will have to manually reconfigure DTU-C 135 and DTU-R 120 by dispatching technicians, which is costly and time consuming.
Accordingly, there is an intense need in the art to reduce the DSL communication systems initial training time, training time for achieving an optimal data rate and providing efficient remote configuration and discovery capabilities.
In accordance with the purpose of the present invention as broadly described herein, there is provided method and system for DSL auto baud or automatic data rate selection.
According to one embodiment of the present invention, a DSL communication system includes a DTU-C and a DTU-R in communication over a communication link. DTU-C and DTU-R are capable of transmitting and receiving packets of data prior to synchronization or training. In one embodiment, a xe2x80x9c1xe2x80x9d data bit is represented by 50 ms of scrambled two level ones and a xe2x80x9c0xe2x80x9d data bit is represented by 50 ms of off-time. DTU-C transmits a discovery message to DTU-R and awaits receiving a discovery response message from DTU-R. After receiving the discovery response message, DTU-C transmits a probe message to DTU-R followed by a probe signal. DTU-R measures the line quality while receiving the probe signal. After receiving the probe signal, DTU-R transmits a probe signal to DTU-C, using which signal DTU-C measures the line quality. After transmitting the probe signal, DTU-R transmits a probe response message, including line quality measurements performed by DTU-R. In one embodiment, the line quality may be based on attenuation level and/or signal-to-noise ratio. At this point, DTU-C and DTU-R may negotiate a first data rate by transmitting data rate messages based on the line quality and/or based on other information that may be exchanged between DTU-C and DTU-R. DTU-C and DTU-R synchronize or train at the first data rate. After synchronization, DTU-C and/or DTU-R measure the line quality at the first data rate. In one embodiment, the line quality may be measured based on bit-error-rate, attenuation level and/or signal-to-noise ratio. A second data rate is then selected based on the line quality measurements. In one embodiment, DTU-C may initiate a rate change request, according to which DTU-C and DTU-R may re-synchronize at the second rate. In one embodiment, the second rate may be several data rates higher or lower than the first data rate.
In another embodiment, DTU-C and DTU-R may measure the line quality at the second data rate and start a re-synchronization process at a third data rate based on the line quality. In yet another embodiment, DTU-C and DTU-R may resynchronize at several different data rates until an optimal data rate is achieved.
These and other aspects of the present invention will become apparent with further reference to the drawings and specification, which follow.